Different types of loading installations are already known for shaft furnaces, especially for blast furnaces. Among these, the “Bell Less Top®” installations are now often used because they allow a better control of the loading of the furnace and the dispersion of the loaded materials. Moreover, the sealing system used in these installations allows a better sealing of the pressurised gases contained in the shaft of the blast furnace, principally due to the functional disassociation between the sealing elements on the one hand and the elements designed to control the introduction of the solids into the furnace on the other hand.
Systems of this type are known for example from U.S. Pat. No. 4,514,129 or WO 2010/081810, and generally comprise a pivotable sealing hatch device, called material hatch, to ensure the closure of one or a plurality of material hoppers and to control the material throughput when the hatch is opened. This hatch device can comprise a single flap or two flaps that pivot in opposite directions.
These systems also comprise a sealing valve, located below the hatch, to prevent the gas leaking from the blast furnace to the exterior. In the closed position the underneath of this valve rests against a fixed seat that is an integral part of the hatch and valve arrangement.
The material hatch and the sealing valve are mounted on a housing of the hatch and valve arrangement, on which is connected a hopper for solid material. This housing comprises a central passage with an essentially vertical axis through which the solid material falls into the interior of the blast furnace onto a distribution screen, according to the technique specific to the Bell-Less Top® system.
In the closed position, the material hatch provides the support for the charge of the solid material contained in the hopper, and the valve provides the gas-tightness.
In the open position, during the introduction of the material into the blast furnace, the material hatch, when pivoted into the open position, allows the material to fall. The sealing valve is then completely removed out of the trajectory of the materials, such that the surfaces of the valve ensuring the gas-tightness are not damaged by the solid materials as they fall into the central passage. When loading, the sealing valve is opened first by a pivoting movement, thereby completely freeing the passage, before the feed hatch is opened for the solid material.
Typically, the pivot axis of the sealing valve is essentially perpendicular to the pivot axis of the flap of the hatch, or to the parallel pivot axes of the flaps. The pivoting movement of the hatch and valve is controlled by the respective actuators attached to the housing of the hatch and valve arrangement. These actuators, which can be of the electric or hydraulic type, such as geared motors or jacks, cause the hatch or the flaps of the hatch and the valve respectively to pivot by means of the transmission shafts that pass through the wall of the housing and which are guided in rotation on said housing by the bearings equipped with sealing means.
In the presently known systems, the bearings are directly fixed on the housing of the hatch and valve arrangement. The flaps of the hatch and/or the valves are integral with said shafts, in the interior of the housing, by means of arms. When the hatch or the valve have to be reached for repairs or replacement, or for restoring the seal, one has to intervene inside the housing. The directly involved personnel enters into said housing through an access manway adapted for this purpose in the wall of the housing and carries out his work in a confined space, and moreover in an environment made hazardous by the heat and the presence of blast furnace gases which still remain in spite of the temporary shut-down of the furnace. This shut-down is required for interventions of this kind, during which there is a loss of production.